arXiv subjects

A. Lenz

Publications and source records attributed to A. Lenz.

23 records · Page 2Linked to original sources

arXiv2003

CP asymmetry in flavour-specific B decays beyond leading logarithms

We compute next-to-leading order QCD corrections to the CP asymmetry a_{fs} = Im(Gamma_{12}/M_{12}) in flavour-specific B_{d,s} decays such as B_d->X l nu or B_s->D^-_s pi^+. The corrections reduce the uncertainties associated with the choice of the renormalization scheme for the quark masses significantly. In the Standard Model we predict a^d_{fs} = -(5.0 +- 1.1)*10^{-4}. As a by-product we also obtain the width difference in the B_d system at next-to-leading order in QCD.

hep-ph↗

arXiv2002

The B^+ B_d^0 Lifetime Difference Beyond Leading Logarithms

We compute perturbative QCD corrections to the lifetime splitting between the charged and neutral $B$ meson in the framework of the heavy quark expansion. These next-to-leading logarithmic corrections are necessary for a meaningful use of hadronic matrix elements of local operators from lattice gauge theory. We find the uncertainties associated with the choices of renormalization scale and scheme significantly reduced compared to the leading-order result. We include the full dependence on the charm-quark mass $m_c$ without any approximations. Using hadronic matrix elements estimated in the literature with lattice QCD we obtain $τ(B^+)/τ(B^0_d)=1.053\pm 0.027\pm 0.017$, where the effects of unquenching and $1/m_b$ corrections are not yet included. The lifetime difference of heavy baryons $Ξ^0_b$ and $Ξ^-_b$ is also briefly discussed.

hep-ph↗

arXiv2001

Light-Cone Sum Rules for the Nucleon Form Factors

We argue that soft non-factorisable terms give a significant contribution to the baryon form factors at intermediate momentum transfers and set up a framework for the calculation of such terms in the light-cone sum rule approach. Among them, contributions of three-quark states with different helicity structure compared to the leading twist prove to be the most important. The leading-order sum rules are derived and confronted with the experimental data.

hep-ph↗

arXiv1999

Next-to-Leading Order QCD Corrections to the Lifetime Difference of $B_s$ Mesons

We compute the QCD corrections to the decay rate difference in the $B_s-\bar B_s$ system, $ΔΓ_{B_s}$, in the next-to-leading logarithmic approximation using the heavy quark expansion approach. Going beyond leading order in QCD is essential to obtain a proper matching of the Wilson coefficients to the matrix elements of local operators from lattice gauge theory. The lifetime difference is reduced considerably at next-to-leading order. We find $(ΔΓ/Γ)_{B_s}=(f_{B_s}/210 MeV)^2 [0.006 B(m_b)+0.150 B_S(m_b)-0.063]$ in terms of the bag parameters $B, B_S$ in the NDR scheme. As a further application of our analysis we also derive the next-to-leading order result for the mixing-induced CP asymmetry in inclusive $b\to u\bar ud$ decays, which measures $\sin 2α$.

hep-ph↗

arXiv1998

Determination of the CKM angle gamma and |V_{ub}/V_{cb}| from inclusive direct CP asymmetries and branching ratios in charmless B decays

We have calculated inclusive direct CP-asymmetries for charmless B^{+/-} -decays. After summing large logarithms to all orders the CP-asymmetries in Delta S=0 and Delta S=1 decays are found as a_{CP} (Delta S=0) = (2.0 +1.2/-1.0)% and a_{CP} (Delta S=1) = ( -1.0 +/- 0.5)%. These results are much larger than previous estimates based on a work without summation of large logarithms. We further show that the dominant contribution to a_{CP} (ΔS=0 ) is proportional to (sin gamma) times |V_{cb}/V_{ub}|. The constraints on the apex (rho-bar,eta-bar) of the unitarity triangle obtained from these two CP-asymmetries define circles in the (rho-bar,eta-bar)-plane. We have likewise analyzed the information on the unitarity triangle obtainable from a measurement of the average non-leptonic branching ratios Br(Delta S=0), Br(Delta S=1) and their sum Br_{NL} (B --> no charm). These CP-conserving quantities define circles centered on the rho-bar--axis of the (rho-bar,eta-bar)-plane. We expect a determination of |V_{ub}/V_{cb}| from Br_{NL} (B --> no charm) to be promising. Our results contain some new QCD corrections enhancing Br(Delta S=1), which now exceeds Br(Delta S=0) by roughly a factor of two.

hep-ph↗